The Surprising Location of Limonene in Pineapple
Limonene is a cyclic monoterpene commonly found in high concentrations in citrus fruit essential oils, contributing to their characteristic fresh aroma. While it's a major component in pineapple, its location is not where many might expect.
The Peel: A Hidden Source of Limonene
Research indicates that high concentrations of limonene in pineapples are primarily located in the peel. Studies utilizing techniques like Gas Chromatography-Mass Spectrometry (GC-MS) have analyzed the chemical composition of oil extracted from pineapple peels. For instance, one study found limonene to be the most abundant compound in Ananas comosus peel oil, making up 76.34% of the total extract. This highlights the peel as a significant, often discarded, source of limonene and other valuable volatile compounds.
The Pulp: A Different Aromatic Profile
The edible pulp of the pineapple has a distinct aromatic profile compared to the peel. The fruit's signature tropical and fruity scent is largely attributed to esters, such as ethyl hexanoate and methyl hexanoate. These esters are the primary contributors to the flavour experienced when eating pineapple, with terpenes, including any trace amounts of limonene, present in much lower concentrations in the pulp. This chemical difference explains why pineapple tastes sweet and fruity rather than tangy and citrusy.
Pineapple's Diverse Volatile Compounds
Pineapple contains a variety of volatile compounds that contribute to its complex flavour.
Esters: These are the most prevalent aroma compounds in the pulp, including ethyl 2-methylbutanoate and ethyl hexanoate, which are key to the tropical flavour.
Lactones: Found in some varieties, lactones like γ-octalactone can provide coconut-like notes.
Terpenes: Beyond limonene in the peel, other terpenes like myrcene (earthy, musky notes) and pinene (piney aroma) are also present in pineapple.
Aldehydes: Compounds such as decanal and nonanal contribute to the overall scent.
Comparison: Limonene in Pineapple vs. Citrus
| Feature | Pineapple (Peel) | Pineapple (Pulp) | Citrus Fruits (Peel) |
|---|---|---|---|
| Limonene Concentration | Very High (often over 75% of peel oil) | Very Low (trace amounts, not a primary flavour component) | Very High (major component of essential oil) |
| Primary Aroma Compounds | Limonene, Myrcene, Pinene | Esters (e.g., ethyl hexanoate), Lactones | Limonene (up to 97% in orange peel oil) |
| Associated Flavour Profile | Fragrant, zesty (if oil extracted) | Sweet, tropical, fruity, tangy | Citrusy, tangy, lemon/orange-like |
| Part Used for Flavouring | Oil extracted for fragrances/supplements | Fresh fruit, juice, pulp | Zest, essential oil extracted from rind |
Why the Distinction Matters
Understanding that limonene is concentrated in the pineapple peel, not the pulp, is significant. Potential benefits of limonene, such as its antioxidant properties, are more relevant to extracted peel oil. This highlights the potential value of pineapple rind as a source of natural compounds. The flavour of edible pineapple, defined by esters in the pulp, is chemically distinct from the limonene-rich peel.
Conclusion: Limonene is a Feature of the Peel
In conclusion, pineapples do contain limonene, but predominantly in the inedible peel, not the juicy pulp. The characteristic sweet, tropical flavour of pineapple comes primarily from esters and other aromatic compounds in the pulp. This difference illustrates the diverse chemical composition within the fruit and the potential for utilizing pineapple waste like the peel as a source of valuable compounds. For further reading, an overview of d-limonene can be found on NCBI.
